1. Field of the Invention
This invention relates to bonded storage disks and, more particularly, to improved methods of and systems for forming bonded storage disk, such as digital versatile disks ("DVDs").
2. Discussion of Related Art
Two popular forms of storage media are compact disks ("CDs") and digital versatile disks ("DVDs"). Each is a form of a bonded storage disk. A bonded storage disk has two or more substrates held together by a cured bonding agent. At least one of the substrates is formed to have "pits," the distribution of which is representative of the information to be stored on the disk. These pits are metallized so that when they are "hit" by an optical signal they will reflect a signal indicative of the pit and thus the information.
Because of their ability to store vast amounts of information, DVDs have been well received in the market. To date, there are four specified DVD formats: DVD5, DVD9, DVD10, and DVD18. DVD5 is a single-sided, single-layered format (see FIG. 1C); DVD9 is a single-sided, dual layered form (see FIG. 1E); DVD10 is a dual-sided, single-layered format (see FIG. 1D); and DVD18 is a dual-sided, dual-layered format (see FIG. 1F). "Single-sided" means that the disk is intended to be read from one side only. "Dual-sided" means that the disk may be read from either side, with each side storing information. "Single-layered" means that for a given side there is one "layer" of information only. In this regard, a layer of information would mean a distribution of metallized pits 4, which when hit with a light source 9 will reflect an information-carrying optical signal. "Dual-layered" means that for a given side there are two layers 4 of information. The specifications are provided in the DVD Book, v. 1.0, by the DVD Forum, which is hereby incorporated by reference in its entirety. The Figures are not to scale. For example, in actuality the substrate 6 is about 0.6 mm thick; for DVD9 the bonding layer 8 is about 50 microns thick .+-.15 microns, .+-.10 microns within a DVD, and .+-.4 microns within a revolution; and the metallization layer 4 is on the order of tens of nanometers.)
The formats specify several, but not all, characteristics of a disk. For example, referring to FIGS. 1A-F, which show a plan view of a DVD and a cross-section view of DVD5, DVD9, DVD10, and DVD18 formats, the formats specify the inner diameter of the center hole, the outer diameter of the DVD, the handling area, the inner mirror band, the data area, and the outer mirror band. They also specify the shape and location of a stacking ring, the pit size, the reflectivity of the metal layers and the type of the metal, and for some formats the thickness and optical characteristics of the bonding agent used to form bond layer 8. In addition, the specifications list acceptable tolerances of certain "bulk parameters," such as "radial tilt" and "tangential tilt." The specifications also specify the thickness of the bonding layer and the acceptable amounts of bubbles and contaminants.
On the other hand, some aspects are undefined. For example, commercially-available substrate molding machines produce substrates having machine-specific moat locations and shapes. In the art, for example, there are known 22 mm moat geometries and 34 mm moat geometries. In addition, though the reflectivity of the metal layers is specified (sometimes by minimums, other times by minimums and maximums) the actual amount of metallization is not.
Typical DVD players include an optical reading mechanism for transmitting an optical signal to a surface of the DVD and for reading a reflected signal. Typically, this mechanism will read a bottom surface of the DVD, as perceived by an end-user and a DVD player. For two-sided formats, the DVD needs to be flipped to read the other side of the DVD. For dual-layer formats, the player adjusts the focus of the optical signal to read a given layer of the two layers of a given side. One orientation is used to illuminate a semi-reflective layer (which would be nearest to the read mechanism) and another orientation is used to illuminate a reflective layer (which would be farthest from the read mechanism). When reading the reflective layer, the optical signal passes through the semi-reflective layer and the bond layer on its way to and from the reflective layer, thus making the bond layer an optical component.
To date, manufacturing DVDs has been problematic, especially for dual-layer formats and especially for achieving desirable yields. In part this is the result of the extremely tight manufacturing tolerances specified by the formats and required by the market. In other part this is due to the complexities introduced with the dual-layer arrangements having the bonding layer be an optical component of a DVD.
Known systems are operating at undesirably low yields. Moreover, due to the difficulty in manufacturing these disks, many if not all DVD manufacturing systems operate as batch processes. These are undesirable because they require partially completed disks to be stored and staged before a subsequent manufacturing step is performed, thus increasing the cost and complexity of manufacturing.
Consequently, there is a need in the art for a system and method that can manufacture DVDs, including dual-layered disks, at high yields. There is also a need in the art for an in-line system that can manufacture DVDs, including dual-layer format DVDs, at acceptable yields.